The present invention relates to scintillation counting, and especially to sample vessels (usually vials) for such counting.
Automated instruments are well-known for measuring the radionucleide content of samples (frequently biological samples) placed in each of a series of vials and mixed therein with a scintillation cocktail. Since the scintillants which emit visible (countable) light in response to radioactive decay are organic-soluble and the samples are generally aqueous, the cocktail typically contains the scintillant, at least one organic solvent and at least one surfactant.
Representative scintillation cocktails are described in U.S. Pat. Nos. 4,443,356 (1984), 4,444,677 (1984), 4,438,017 (1984).
Vials for such counters are traditionally glass, and must be carefully washed between uses to avoid various types of cross-contamination. While disposable polyethylene vials have been suggested and used, they have three major drawbacks compared to glass: (1) permeation of organic solvents leading to objectionable or even potentially toxic vapors in parts of the laboratory generally not equipped with proper airflow or hoods for such vapors, (2) swelling or deformation of the vials so as to jam or stick when being automatically inserted into or removed from the counting well, and (3) adherence of biological matter to the inner surface of the vials so as to either interfere with emitted light or to overcome the intimate mixing of organic and aqueous phases required for efficient energy transfer (scintillation efficiency).
Various materials other than glass or polyethylene having been suggested for such vials. In U.S. Pat. No. 4,021,670 to Noakes (1977), various plastic such as "nylon, linear polyethylene and the fluoroplastics (Teflons)" are mentioned. Polytetrafluoroethylene (sold by Dupont under the registered trademark "TEFLON") is difficult to shape (is not melt processable) and is expensive, such that disposable PTFE vials would not be practicable. Nylons (polyamides) would probably swell worse than polyethylene, suffering from both the aqueous and the organic contents. See also Chem. Abstr. 93: 103429W.